Insights into the role of RapA, a rhizobial extracellular lectin involved in biofilm formation.

ABDIAN, PL.; VOZZA, N.F.; RUSSO D.M.; CARAMELO J.J.; ZORREGUIETA A.

Mar del Plata

Congreso; LI Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB).; 2015

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Under nitrogen starvation, rhizobia establish symbiotic interactions with legumes inducing the formation of root nodules in which conversion of atmospheric nitrogen to ammonia takes place. In Rhizobiumleguminosarum, it has  recently been shown that attachment to roots hairs, increased biofilm formation and nodulation competitiveness are primarily due to enhanced expression of the Rap proteins (Rhizobiumadhering-proteins).Among them, we have characterized RapA, a unipolar calcium-binding lectin. RapA is secreted by the type I PrsDE system and is composed of twoRa/CHDL (cadherin-like) domains that specifically recognize the acidic polysaccharides produced by R. leguminosarum. The exopolysaccharide (EPS) and capsular polysaccharide (CPS) are structurally and genetically related, and are important components of the biofilm matrix. In this work, we show that increased levels of RapA enhance in vitro biofilm formation but disrupt intimate cell-cell interactions in the biofilm. An examination of the polysaccharides produced by the rapA mutant and overexpressing strains revealed an alteration in the balance between CPS and EPS production. Interestingly, we also observed that the cleavage of EPS isaltered by increased levels of RapA, giving rise to a particular distribution of EPS molecule sizes. We propose that the RapA lectin is important in the remodeling of the biofilm EPS-matrix.